1. Field of the Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a method for removing carbon-rich particles adhered on a metal surface, especially on the exposed copper surface of a copper/low k dielectric dual damascene structure.
2. Description of the Prior Art
When the semiconductor process steps into the stage of deep-submicron, it is a trend to employ a Cu damascene process combined with a low k material as an interlayer dielectric to effectively reduce RC delay and improve electromigration property. FIG. 1A shows a typical copper/low k dielectric dual damascene structure. A semiconductor substrate 100 having a substructure comprising devices formed in the substrate and a metal layer formed thereon (not shown in the figure) is provided. And, a barrier-CMP stopping layer 104 formed of silicon nitride (Si3N4)/or silicon carbide and a barrier layer 106 of Ta/or TaN are inter-layers between a low k dielectric layer 102 formed on the substrate 100 and a copper layer 108. The barrier layer 106 is served for preventing copper diffusion to the low k dielectric layer 102.
Referring to FIG. 1B, during the copper/low k dielectric dual damascene process, a copper chemical mechanical polishing process is firstly applied to planarize the copper layer 108 inlaid into the trench 112 and via hole 110 structures of the low k dielectric layer 102, until the barrier layer 106. Then, a barrier chemical mechanical polishing process is followed to remove the barrier layer 106 until the stopping layer 104. However, the softer copper metal typically polishes back at a faster rate than the surrounding material and then causing dishing in the copper layer 108, as shown in FIG. 1B, the CMP copper layer 108 is provided with a dished structure below the dotted line of the top surface thereof. The low k dielectric layer 102 is easily exposed and then polished during the two CMP processes, due to the dishing phenomenon of the copper layer 108, even though the barrier-CMP stopping layer 104 is applied on the low k dielectric layer 102. The low k dielectric generally carbon-rich, containing at least 90% carbon element, and copper metal and carbon element have reverse electricity in a neutral/or acidic slurry employed in the copper CMP and barrier CMP processes. Therefore, there are many carbon-rich particles produced and adhered on the exposed copper surface of the copper layer 108 inlaid into the trench 112 and the via hole 110, during the two CMP processes, which results in a process defect.
Accordingly, it is desirable to provide a method for effectively remove carbon-rich particles adhered on a copper surface, especially on the exposed copper surface of a copper/low k dielectric dual damascene structure, and then alleviate the drawback of the conventional CMP process for copper/low k dielectric damascene process.
It is one object of the present invention to provide a method for removing carbon-rich particles adhered on a copper surface, especially on the exposed copper surface of a copper/low k dielectric dual damascene structure. After a Cu-CMP process and barrier CMP process are completed, a chemical buffing polishing process under a downward force of about 0.5 to 3 psi, using an acidic aqueous solution, is applied on the exposed copper surface to effectively remove carbon-rich particles adhered thereon, which is due to the low k dielectric layer containing at least 90% carbon element being exposed and then polished during the two CMP processes, coming from a dishing phenomenon of the copper layer.
It is another object of the present invention to provide a method for removing carbon-rich particles adhered on a copper surface, especially on the exposed copper surface of a copper/low k dielectric dual damascene structure. After a Cu-CMP process, a first chemical buffing polishing process using an acidic aqueous solution is followed, and a second chemical buffing polishing process using an acidic aqueous solution is applied after a barrier CMP process. Both of the two chemical buffing processes are used to remove carbon-rich particles adhered on the exposed copper surface during the two CMP processes.
It is a further object of the present invention to provide a method for removing carbon-rich particles adhered on a copper surface, which is suitably applied to a low k material chemical mechanical polishing process.
In order to achieve the above objects, the present invention provides a method for removing carbon-rich particles adhered on a copper surface, especially on the exposed copper surface of a copper/low k dielectric dual damascene structure. Firstly, providing a semiconductor substrate having a substructure comprising devices formed in the substrate and a metal layer formed thereon. Then, forming a low k dielectric layer over the substrate. Subsequently, forming a stopping layer on the low k dielectric layer. Thereafter, patterning the stopping layer and the low k dielectric layer to form a plurality of via holes for interconnects, and then patterning the stopping layer and the low k dielectric layer to form a plurality of trenches for conductive lines. Afterward, forming a conformal blanket layer above the patterned layer of the stopping layer and the low k dielectric layer as a barrier layer. Following, forming a copper layer over the barrier layer to fill the via hole and the trench. Then, performing a copper chemical mechanical polishing process to planarize the copper layer until the barrier layer. Subsequently, performing a barrier chemical mechanical polishing process to remove the barrier layer until the stopping layer. Following, performing a chemical buffing polishing process under a downward force of about 0.5 to 3 psi using an acidic aqueous solution to remove the carbon-rich particles adhered on the exposed copper surface of the copper layer filled in the trench and the via hole. Finally, performing a post chemical mechanical polishing cleaning process to remove away dirt left on the exposed copper surface. Alternately, a first chemical buffing polishing process is applied after the Cu-CMP process, and a second chemical buffing polishing process is performed after the barrier CMP process.